1. Field of the Invention
The present invention relates to an improved device for coupling the pistons to the rotor in a radial-piston hydraulic motor in which the peripheral surface of the rotor has a spherical shape.
2. Prior Art
As is known, hydraulic motors of the aforementioned kind comprise a housing containing a rotor having a spherical surface and eccentrically mounted on the driving shaft and secured thereto, the motors also comprising a number of hydraulic pistons radially disposed around the rotor, one end of each piston being in permanent oscillating contact with corresponding bearing seats formed in the inner walls of corresponding radial cavities associated with the motor housing, whereas the other end is in sliding contact with the spherical surface of the rotor and held in contact therewith by a pair of coupling rings disposed at the sides of the rotor and engaging the aforementioned end of each piston. The hydraulic fluid is distributed to the radial pistons in known, conventional manner, via that end of each piston which is in permanent oscillating contact with the respective cavity associated with the engine housing, corresponding to the respective bearing seats. In a known type of motor, hydraulic pressure fluid is driven through the cavities in the piston directly against the spherical end of the rotor, where it is retained by the outer edges of the corresponding end of the pistons, which slide in contact with the spherical surface of the rotor.
Normally, sliding contact between the ends of the radial pistons and the spherical rotor surface is maintained by a spring means which is inserted between the telescopically-movable components of each radial piston.
In the case of the aforementioned kinds of motors, however, it has been found necessary in practice to provide additional means for ensuring contact between the radial ends of the pistons and the underlying spherical surface of the rotor since temporary negative pressures may sometimes occur inside the pistons and raise their ends from the spherical surface of the rotor against the action of the spring, thus endangering the radial seal of the hydraulic fluid and preventing proper operation of the motor.
To avoid this disadvantage, it has already been proposed to couple the end of each radial piston to a pair of rings concentric with the rotor and placed on each side of it, so as to permanently secure the pistons to the spherical surface of the rotor.
In the prior art, the rings, which are secured at the sides of the rotor, engage corresponding projections formed directly on the end of each radial piston.
In practice, however, the aforementioned coupling devices have a disadvantage in that the stresses transmitted by the end of each radial piston to the corresponding coupling rings are excessively concentrated in regions of limited area, which results in excessive forces being concentrated on the rings and possibly deforming them.
According to another feature of the prior art, the coupling device the ends of the pistons and the spherical rotor surface does not leave the end sufficient freedom relative to the spherical surface, and this results in excessive wear since the end always slides on the same portion of the spherical surface.